POS0392 ROLE OF SEMIQUANTITATIVE THIGH MAGNETIC RESONANCE IMAGING (tMRI) IN DETERMINING SKELETAL MUSCLE OUTCOMES AT BASELINE AND ON FOLLOW UP IN IDIOPATHIC INFLAMMATORY MYOPATHIES (IIMs)
Authors: M. Gorijavolu, D. Bairwa, C. Kavadichanda, A. Gopal, S. K. Dunga, M. M. Thabah, V. Negi
Journal: Annals of the Rheumatic Diseases (2022)

Background Idiopathic Inflammatory Myopathies (IIMs) are characterized by muscle inflammation and associated muscle weakness. Semiquantitative scoring of thigh Magnetic Resonance Imaging (tMRI) has shown contradictory results in associating muscle inflammation, damage, and clinically assessed muscle weakness. Moreover, there are no studies assessing the role of tMRI detected muscle damage in determining long-term recovery of muscle strength and endurance. Objectives To correlate tMRI scores for muscle edema, fascial edema, muscle atrophy, and fatty infiltration with consecutively collected manual muscle testing 8 (MMT-8) scores and muscle enzymes. To determine the role of baseline tMRI changes in achieving maximum muscle power during follow-up. Methods This is a retrospective analysis of a single-center myositis cohort. IIM patients (n=55) who underwent baseline tMRI (STIR and T1 sequences) at the time of diagnosis were included. Baseline demographic, clinical, and serological parameters were noted. MRI T1 weighted sequence and STIR sequence axial and coronal images were assessed for intramuscular and fascial edema, atrophy and fatty replacement using a semiquantitative score and the percentage of muscle involvement for each parameter was calculated. MMT-8 values and muscle enzyme levels which remained unchanged at least for 6 months during follow-up were noted for 42 patients. MMT-8 ≥74 was taken as near normal muscle power based on the fact that 75% of IIM patients in remission for a long duration achieved MMT-8 of≥74 in our cohort. Spearman correlation was done between clinical parameters, muscle enzymes, and tMRI scores. Baseline parameters of patients who achieved and did not achieve MMT8≥74 were compared. Multiple linear regression was performed to assess the tMRI variables predicting a higher MMT-8 during follow-up Results The median age was 36 (27.25-44.75) years, median duration of disease at presentation was 4 months (2-10), median duration of follow up was 24 months (6.75-38.25). Dermatomyositis, Polymyositis and Antisynthetase syndrome comprised of 58.2%, 7.3% and 30.9% cases respectively. Baseline muscle enzymes CPK(r=0.531), AST(r=0.535) and ALT(r=0.442) showed significant positive correlation(p&lt;0.01) with muscle edema. Baseline MMT-8 showed significant negative correlation with muscle edema(r=-0.657) and fascial edema(r=-0.522) (p&lt;0.01). Follow up MMT-8 showed significant negative correlation with muscle edema(r=-0.359), muscle atrophy (r=-0.319) and fatty infiltration(r=-0.308) (p&lt;0.05) (Figure 1). Baseline MMT-8 and MRI fatty infiltration were significantly different between patients who achieved and did not achieve MMT-8 of ≥74 on follow-up (Table 1). Multiple regression analysis revealed adjusted R 2 value of 0.386. Baseline MMT-8(β=0.372) and muscle atrophy(β=-0.459) significantly predicted MMT-8 on follow-up Table 1. Comparison between those who achieved near-normal muscle power versus others Follow up MMT-8&lt;74 (n=8) Follow up MMT-8 ≥74 (n=34) P-value Age (years) (median, IQR) 36.5(27-47.5) 36(28.75-44.25) 1.000 Duration of disease (months) (median, IQR) 6(4-10.5) 3.5(2.75-9.75) 0.459 Baseline muscle enzymes and MMT-8 (median, IQR ) CPK (IU/L) 1758(116-6160) 680(57.5-3595) 0.410 LDH (IU/L) 496(240-823) 616.50(289.25-753) 0.672 AST (IU/L) 112(76-201.5) 69.5(40.5-226.25) 0.352 ALT (IU/L) 74.50(65.5-139.75) 69(36-142.25) 0.560 MMT-8 baseline (0-80) 49.5(47.25-56) 63(53.75-73.25) 0.007 MRI thigh scores (median, IQR ) Muscle edema% 22.41(5.65-63.33) 10.37(0.00-28.70) 0.070 Fascial edema % 43.33(18.61-78.06) 33.89(11.49-50.56) 0.478 Muscle atrophy % 2.22(0.28-20.83) 0.00(0.00-2.50) 0.081 Fatty infiltration % 6.67(2.78-18.61) 0.56(0.00-3.61) 0.010 Figure 1. Correlation between baseline and Follow up MMT-8 with tMRI scores. Conclusion Low baseline MMT-8 and presence of muscle atrophy at baseline are predictors of poor outcome. Hence performing a baseline MRI will help in the prognosis. Disclosure of Interests None declared